It is recommended that you include enough questions to obtain all of the information needed at one time. Using items that are short, concise, clearly written statements that get right to the point will only take seconds to read and rate. A 20 item survey should require about 5 minutes for someone with an 8th grade reading level.
Customer surveys should not contain more than 30 questions without offering an incentive to compensate participants for their time. Employee surveys may be longer without impacting response rates or requiring an incentive. A typical employee survey includes 40-60 questions.